[BMJ]

I'm messin with my Avy Woodie's compression circuits and was wondering your thoughts on the interaction of the separate HSC and LSC circuits.

Can one assume that by closing down the LSC circuit that it would make the HSC circuit more active? Would this mean that the HSC would blow open sooner and stay open longer unless you add more HSC preload to slow it down?

 

[FM]

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The way the Avy controls work is different than on other shocks and forks. I thought I had a pretty good understanding of the basic concepts of HS- and LSC, but getting the avy tuned in had me stumped.... until I called Craig and realized I had the adjustments backwards!
:lol:

Anyways I'd definitely call Craig and have him talk you through the tuning process. He's very patient and 5 minutes talking with him had me straightened out.

As I recall their is some overlap between the adjustments, so if you have either totally open, neither work.

 

[derby]

I'm messin with my Avy Woodie's compression circuits and was wondering your thoughts on the interaction of the separate HSC and LSC circuits.

Can one assume that by closing down the LSC circuit that it would make the HSC circuit more active? Would this mean that the HSC would blow open sooner and stay open longer unless you add more HSC preload to slow it down?

I don’t know the answer from experimentation. But I think you are correct in your assumption.

One of the shock and fork techs working at PUSH once mentioned to me that by slowing the rebound (LSR) adjuster on a Pike fork, the HSR would open sooner and become faster. PUSH only tunes the rebound of Pike forks and leaves compression (Motion Control) stock. I tried that briefly and the fork was still to slow overall for my liking mainly from firm compression even with a light spring, so I changed oil from stock 5w to 2.5w and found the tuning range for low and high shaft speed action was more active and had a faster range of tuning for both compressing and rebounding. With the lighter oil rebound was still too slow for my style when firming up the LSR adjuster more than about 50%.

If the Avalanche is typical, and I think it is, the LSC circuit is an externally adjustable size orifice port straight to the reservoir, bypassing the main shim stack HSC circuit to the reservoir. With both open the HSC has much less than 100% flow to open the shim until a fast enough flow speed where the LSC hydro locks and nearly 100% flows through the HSC. Percent flow to each circuit varies by flow (shaft) speed.

If you block off the LSC, 100% flow goes all through the HSC with any flow speed. So the HSC shims must begin to open sooner, and become fully open sooner, and close later with a given rate of flow speed acceleration and deceleration, compared to also having the LSC to allow some of the flow bypassing HSC at lower flow speeds.

Maybe an expert could reply and add some tuning tips to help you alter your compression shims in the right direction for what you want different.

 

[FireDog46]

This is how it was explained to me

The HSC determines the working range of the LSC.

My e-mail to Craig:

I just received my Chubie with the optional Hi/Low compression adjuster.
I'm having a little trouble understanding the two circuits.
Unfortuantely it will be awhile before I get the bike completed,
so it will be sometime before I can experiment with damper settings.
I have downloaded the manual and I have read the FAQ.
I always thought low speed compression helped control pedal input
as well as undulating terrain input and high speed compression
provided for small/large bump and square edge hit compliance. You describe
using the high speed adjuster to control pedal input. This seems
to be the reverse of everything I have read elsewhere.

My thinking would be to use the low speed adjuster to establish
a balance between pedal input and undulating terrain and use
the high speed adjuster to establish a balance between small and
large bump hits and square edge hits.

Craig's response

Yes, all you said is true, but in order to give the low speed circuit the
most damping, the high speed circuit must remain closed, if the hi speed
adjuster is set full soft the 4 holes it controls will be open, thus
decreasing the low speed damping by 400 %. If pedaling is the only concern
set the high speed to full hard so it stays closed, if there are high speed
bumps that need to be absorbed then open the high speed up a little, but if
you open it to one turn from all the way out it will also open more holes
which will affect the low speed circuit too.

 

[nybike1971]

FireDog,

Thank you for posting that e-mail communication, it i extremely valuable. I kind of reached the same conclusion after trial and error but it's nice to see it in writing and to understand why.

 

[BMJ]

Great info guys, keep it commin!

 

[FM]

Yeah thanks for sharing that firedog!

Adding a bit from their FAQ to this thread:

>15. Whats up with your high/low speed remote compression adjuster. How does it work?
The remote hi/low speed adjuster has a low speed needle and a high speed blow off valve and as you adjust the screw tighter it increases the low speed compression and also increases the preload force on the blow off valve thus giving the shock more high speed compression. If the shock experiences a large high speed hit it will still blow off to prevent harshness and prevent the shock from hydraulic lock (keeps the shock from blowing up).
You can run the adjuster at full hard to simulate lockout and this improves pedaling while still absorbing larger hits.

 

[derby]

Yeah thanks for sharing that firedog!

Adding a bit from their FAQ to this thread:

>15. Whats up with your high/low speed remote compression adjuster. How does it work?
The remote hi/low speed adjuster has a low speed needle and a high speed blow off valve and as you adjust the screw tighter it increases the low speed compression and also increases the preload force on the blow off valve thus giving the shock more high speed compression. If the shock experiences a large high speed hit it will still blow off to prevent harshness and prevent the shock from hydraulic lock (keeps the shock from blowing up).
You can run the adjuster at full hard to simulate lockout and this improves pedaling while still absorbing larger hits.

Looking at the assembled Low/Hi valve, it’s not conventional - well there’s not a shimmed valve for HSC. Its spring loaded which may be very conventional too, I don’t really know what is common and conventional I’m not highly experienced about shock internals.

Looking at the assembly, it looks like blocking off the LSC by turning the needle screw in to close the circuit would force all flow to push the HSC piston open wider, loading the spring more, than if the LSC was flowing even a little. I guess that’s what he means by “as you adjust the screw tighter it increases the low speed compression and also increases the preload force on the blow off valve”.

I think the OP’s original assumption would still be true. And with LSC blocked off the HSC would open wider and the swingarm would compress deeper into travel, compared to using both LSC and HSC circuits, from the same sharp hit. But the same sharp hit with LSC blocked off would feel sharper, harsher even though there is deeper swingarm travel. Using both LSC and HSC with a good balance of both would make smoother, progressive, and slightly shallower compression resistance to the same sharp or heavy compression hits.

 

[FM]

Most excellent thread

I've gotten my avy tuned in nicely, but the inner workings have been somewhat of a mystery to me. This thread has really helped me understand how the shock works.

I put all the info here and some off the avalanche website into this jpg. I'll be printing this out and putting it up near my repair stand

 

[BMJ]

Howz this question.

I've read on a thread about the CCDB that if you have the HSC circuit wide open that it effects the main shim stacks ability to open properly.

The question is this...would this be due to the fact that the CCDB circulates the fluid vrs displaces it like in the Avy shocks? Would a certain amount of HSC compression adjusted in the firmer position have the same affect on the Avy's?

Reason why I ask is I get this odd sensation that if I fully firm up my HSC circuit, it almost seems as though the shock blows through it's travel faster if I jump on it hard. Maybe it's just cycological.



I guess it's like this. If more LSC makes the HSC circuit open sooner, would more HSC make the main shim stack open sooner?

 

[derby]

I've read on a thread about the CCDB that if you have the HSC circuit wide open that it effects the main shim stacks ability to open properly.

I guess it's like this. If more LSC makes the HSC circuit open sooner, would more HSC make the main shim stack open sooner?

I was thinking of commenting on the CCDB’s somewhat similar LS/HS tuning after looking closely at the Avalanche for my interest in learning more. Thanks for the question!

The Avalanche shocks probably have a shimmed main chamber piston. Below is a diagram of a Penske shock with a most common design using shimmed main piston with a rebound tunable size orifice bypass to tune low speed rebound damping.

There are shims on both sides of the main chamber piston, one set for rebound and one set for compression. I could be wrong about this being the Avalanche design, there’s no diagram I can find for the Avy main chamber, but looking at other similar shock diagrams having LSC/HSC tuning assembly in the flow to the reserve chamber, I have a good huch the Avy is very similarly usiong main piston shims for rebound and probably also for compression.

In the Avalanche (unlike the CCDB and similar RS Vivid) there is a small volume flow into the reserve chamber that is highly “leveraged” by the shaft displacement of fluid from the main chamber during compression, and this flow is restricted and tuned by the LSC/HSC assembly. My guess is that the compression side shims on the main chamber piston produce the main effect of HSC damping in the Avy. I’ll also guess that the LSC screw mainly tunes LSC, and the HSC bolt preloading the spring affects more medium speed transition into high speed damping as well as giving the blow off ability for very sharp big hits, so that high speed damping is mainly damped by the main piston compression shims when the HSC adjustment valve blows open.

Turning both LSC and HSC to max firm in the AVY still allows the HSC adjuster valve to blow open (or the shock would blow up!). When it blows open the main piston shims are all that’s really doing any damping, and the action is probably very platform like loading up the suspension and suddenly digressive or falling rate in “damping” resistance, and very compliant which plunges the travel deeper than a more balanced LSC/HSC tune that produces more linear or rising rate effect in compression resistance.

The CCDB is a high flow system with no main piston dampening shims, except one very firmly preloaded blow off compression shim for the sharpest big hits to avoid high speed flow hydro lock. In the CCDB both compression and rebound LS/HS assemblies appear to be very similar in design to the Avalanche LSC/HSC assembly, except the HS valves in the CCDB appears to use an adjustable spring loaded single shim rather than the Avalanche’s in a HSC tuning/blowoff spring backed piston-like valve with ports allowing tunable transition to blow-off. I’ve included pics of the CCDB adjusters and main chamber twin-tube design diagram after the first diagram of what I think the Avy main chamber is designed similar to.

The CCDB has no internal fine tuning potential. The Avalanche can be fine tuned internally to be more specific for rider weight and use. The Marzocchi World Cup and discontinued ’02 to ’04 Fox Vanilla RC damping are similar to the Avalanche design except there is no HSC external adjuster.

 

[Jayem]

The Avalanche shocks probably have a shimmed main chamber piston.

Yep, here's the picture (from an older avalanche DHS shock though).

except the HS valves in the CCDB appears to use an adjustable spring loaded single shim

My understanding is that it's a spring-loaded poppet valve (seems to be supported by the picture). I'm not sure what you mean by "shim" in the quote above, whether you're referring to damping by a shim that flexes to allow oil to bypass (traditionally what a "shim" is for when talking about a damping device) or whether it's just functioning as a poppet-valve.

 

[BMJ]

How bout this....

First, my thought on that shim....

The single shim at the bottom of the CCDB hi/lo adjuster is controlled by the wave spring. This is found in the Avy design as well and closes down the bypass ports upon compression forces but opens freely to allow the fluid to bypass the circuit going in the other direction.

Now my newest question-

I had a thought about how the hi/lo adjustments might affect the main shim stack in the Avy. If the settings where too light, would that mean that the main stack wouldn't open properly and would rather "plow" the oil into the resevoir chamber until hydrolocking both circuits and then forcing the main stack open untill the forces are equalized and than the flow could continue into the resevoir properly?

I'm beginning to realize that it may not be as easy as just turning one or the other adjuster. It's looking like a fine art of balance!:madman:

 

[MK_]

The CCDB has no internal fine tuning potential.

That's not quite correct. CCDB can be tuned by replacing the poppet valve springs with ones of different rates. Currently you preload those coils to achieve specific damping characteristics, and while it appears to work very well, you could squeeze a little more performance by getting a specific spring in there for a given rider/frame/style.

You could potentially tune the blow off, as well, as you call it, by adjusting the shim stack. That wouldn't do a whole lot, anyway, as that's not really there to provide any damping, per se.

_MK

 

[rscecil007]

Here's some more chat about HS/LS interaction, but most is based on the CCDB.

linky

 

[derby]

First, my thought on that shim....

The single shim at the bottom of the CCDB hi/lo adjuster is controlled by the wave spring. This is found in the Avy design as well and closes down the bypass ports upon compression forces but opens freely to allow the fluid to bypass the circuit going in the other direction.

Now my newest question-

I had a thought about how the hi/lo adjustments might affect the main shim stack in the Avy. If the settings where too light, would that mean that the main stack wouldn't open properly and would rather "plow" the oil into the resevoir chamber until hydro locking both circuits and then forcing the main stack open untill the forces are equalized and than the flow could continue into the resevoir properly?

I'm beginning to realize that it may not be as easy as just turning one or the other adjuster. It's looking like a fine art of balance!:madman:

The spring loaded piston with holes of the Avy’s HSC damper is actuated only by the fluid volume displaced from the compressing shaft, so a very small but highly pressured fluid volume. The shimmed main chamber piston is mainly handling HS damping all the time, the HSC adjuster tunes and supports the mid-speed transition and high speed damping in combination with the fixed rate of damping by the internal shims on the main piston. When the shaft compression speed is so fast that the fluid flow opens the HSC piston wide, the flow past the shimmed main piston bends the shims also to relieve flow resistance. Firmer HSC damping adjustment won’t affect extra sharp hits much, that is beyond the range damping is useful unless tuned internally with firmer main piston shims for limited extremely harsh use, such as the harshest WC downhill courses or Red Bull Rampage huge drop types of expert extreme riding.

The CCDB spring loaded HS washer/shim in both the compression and rebound is actuated similarly but by the relatively low pressure but high volume of fluid moved mostly by the piston in the main chamber plus the fluid displaced by the shaft. The much higher volume of fluid flow through the CCDB HSC will have drag effects around the spring loaded washer/shim. The design could have used a solid or ported piston if they didn’t want the specific flow effects of fluid washing around the washer/shim. Washers are more flexible than a solid piston and would have some more cushioning when closing suddenly. Since the washer would act like a shim I think its OK to call it a shim.

For balancing LSC and HSC I have no hands on experience with. For shocks where there is just LSC to externally adjust I’ll start with the compression adjuster set full soft and first test ride to adjust rebound damping to settle bump rebound and wallow to a minimum without feeling firm riding, this is normally near the middle of the adjustment range. Followed by increasing compression one click at a time to give good handling balance with the fork’s compression rate in corners, and combined with fork compression firmness for ramp up support with the spring for easier jump landings and overall firmness for the ride conditions. I’ll use softer compression for slower and rougher conditions and a click to a few clicks firmer for higher speeds and smoother slow ride conditions.

My guess for separately adjustable LSC/HSC is this. After setting rebound action first with compression set to max soft, I’d leave HSC max soft and work with LSC with the same objects as in the previous paragraph. I’d increase HSC to add more support to avoid bottoming harshly without changing springs for hard jump landings such as to flat or high speed riding on roller coaster terrain. For the most part I’d guess I’d stay in the softer third of adjustment range for both the LSC and HSC, and use a similar adjustment within in range for each, then tweak one or the other slightly from there and ride for a while to learn to sense the effects.

For bikes which bob a lot when pedaling I’d set LSC near the middle of range and HSC closer to middle range also to keep the transition to HSC progressive, then lower both until small bump compliance is better and bob isn’t bad with a good pedal technique.

Someday I hope to have a shock with separately adjustable LS and HS damping to test my guesses on setup.

Maybe someone with some years of experience with Avalanche shock tuning can chime in and offer some well balanced suggestions for different conditions.

 

[Jerk_Chicken]

Dear Derby,

You still don't know how the CCDB works.

Love,

Jerk Chicken